DIY Audio Projects Forum

Hello,

The design allows for one power supply for both B+ and the heaters. Anything over 13 volts will need a separate power supply for the heaters. Also you will have to change the Anode resistors to approx 12k. The mosfets and the regulators will need to be heatsinked as they are running the amp in class A and will get very hot. In short, it is possible, but not practical in this configuration.

The sound does open up with higher voltage, but this amp is designed to be a very simple amp, with decent sound. Something a new builder can put together and enjoy.

The sound is quite remarkable for such a simple amp. It is warm, yet has enough punch for popular music. I increased the input capacitors to 2.2u to allow for better bass response.

If you are looking for an amp to match your power supply I suggest the MHHA http://www.headphoneamp.co.kr/bbs/zboar ... asc&no=217

This is an amp built by Sijosae, I built many of his designs back in the day. The website is in korean, but you can easily convert it with google translate.

Thanks

Rogers

(1) Sure; you'd need a third LM317 as a voltage regulator, setup to regulate to
around 12.6 (+/- around .4 volts...). The filament on the 12AU7 is 12.6V; probably
shouldn't go over around 13 volts for better filament life...

(2) Heh - I'll find out how it sounds in a few more hours of work! Holes drilled, layout decided upon,
there's not much to put in - it's a nice, simple build, but I'll have some photos of mine, I hope....

Mike Yancey
Dallas, Texas

Thanks for putting this project up!

Built mine over the week and was able to learn much about tube amps from this project (my first project being a CMoy and the rest are projects which have ready made PCBs and liitle work was needed to understand the schematic, just stuffing the components and soldering).

Got mine built on a project board and blew a cheap china 12AU7 tube the first time after i got the wiring wrong for the heater and mosfets. Redo the amp and at the second attempt I have sound at the left but not from the right. Ordered a set of new IRF510, LM317 and rebuilt it again following the layout and wiring traces as per the PCB for the project and its alive! It sounds great with a RCA 12AU7A tube!

Here's a picture of what it looks like now, will be looking at casing it and also heatsinking the mosfets.

Keechoon,

Great job, looks good. Will like to see your enclosure when you finish.

Also if you cant seem to find an enclosure, you can line up the socket pins onto holes in your proto board, mark with a marker and dremel the holes. This will allow you to mount the tube socket directly onto the board and use the board as is. As you see on my design, i left it open for ventilation and also it displays a very "techie" aesthetic.

Everyone,
As you learn more about tubes, it is important to reference tube charts to determine the correct gain, and voltage swing. Here is a program that will chart the load lines lines for you (loadlineplotter) . Thanks to the Valve wizard for a very useful program http://www.freewebs.com/valvewizard/links.html. His site has great examples of common tube circuits.

For those new to load lines, this website give a funny but down and dirty explanation. http://diyparadise.com/tubeloadline/tubeloadlines.html

hi, i am new to building and soldering pc boards. i love tubes and the sound produced by tubes. i am definitely thinking of building this and have a few questions on it. first, i know what a R1 100k, 1/4W is ,but what is a 150, 1/4W?? i cant find this on the radio shack website at all including the 10, 1/4W. the other things are located in radio shack but id dunno what a 150, 1/4W or a 10, 1/4W is. if you can explain if it is a resistor and why it doesnt have a K at the end, please explain to me. thanks! onother question is that the resistors, do they have to be metal-film? if so which ones? thanks so much!! i love the concept!!!

Pat

Hi Pat
the k is for thousands so if it says 1k it is 1000 ohms. So 10 would be actually 10 ohms and 150 is 150 ohms which are not very popular resistors at most places

in the UK Maplins have all the values for the caps and resistors which i was surprised at

other examples are 4k7 or 4.7k which would be 4700 ohms

they don't have to be metal film carbon will do you can always source better caps and resistors later and replace as necessary and 1/2 watt is ok the caps can be higher in voltage but not lower

don't forget that the 2.2uf caps are bi-polar meaning it has no polarity so it can go either way round the rest have a negative side and have to follow the correct polarity on the board eg + to + - to -

hope that helped
Koogar

_________________
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NP-100v12 - 12AU7 / IRF510 HeadAmp

150 ohm resistors should be readily available, as they're in the 10%, 5% and the 1% tolerance series of resistors.
Take a look at a list of the 'standard' E6, E12 or E24 series:

http://www.logwell.com/tech/components/ ... alues.html

Hopefully 150 ohm's pretty common; however, two 300 ohm in parallel would do as well!

I've found 2.2uf caps (and 2uf and 1uf) in mylar or 'film' capacitors.
By 'non-polar', he's basically meaning DO NOT use an electrolytic or tantalum (like this one):

http://www.allelectronics.com/index.php ... uf&x=0&y=0

Something LIKE this (from Digikey) IS what to use:

http://search.digikey.com/scripts/DkSea ... 95-1126-ND

However, I'll confess, I'm attempting to use ONLY what I have on hand, so I've substituted a 1.0uf for the 2.2uf for now; probably swap it out later.

Almost finished, too. I've got some final assembly and pre-connection testing to do.

Mike Yancey
Dallas, Texas

Thanks everyone for the explanations, Pat, if you pick up this pack Part # 271-309 from Radio Shack. It will include the 100k, 10, 150 and 4.7k (4k7) that are used in the amp. The pack is about $5 and they are all metal film. Metal film is not necessary, just that this is a convenient pack to get them all at once. There are arguments that metal film is sonically superior, but since this amp is operating at such a low level the difference is negligible.

A 4.7K can be used in place of the trim potentiometer to set current through the tube and the bias for the mosfet. 4.7k will set the bias at around 6~7 volts.


The wonderful thing about this amp is you can use pretty much what you have. You can get away with a 100 ohm cathode resistor, if using a trim pot at the anode, just adjust until the gate of the mosfet is half of the B+. Heck you can even omit the cathode resistor if you do not have one. The amp can run straight common cathode, but I have decided on 150 because of the bias point and there are some in the radio shack multipack.

Have fun
Rogers

All,

Most of the values in the amplifier are not set in stone. The amp is designed to be a bit flexible, but I gave values that provide the best sound reproduction and are easily obtainable. Changing the values a bit will change the frequency response and the gain a little, but will not damage the amplifier. Just ensure to feed the heaters between 12~13 volts.

C1: 1.0uF or higher. Anything lower will cut the bass significantly. If you use a polarized electrolytic, make sure the (+) leg is toward the tube.

C2: ~47uF to 220uF

C3: ~20uF to 1000uF

R1: ~100k to 1M

R2: ~50 to 200 ohms

R3: best at 4.7k

R4: best at 10 ohms

R5: ~220 ohms to 1k

Tube: 12AU7, ECC82, 5695 or even a 12AT7 (higher gain). 12AX7 has too high a mu and sounds horrible.


Have fun, Rogers